Final answer:
The diagnostic feature of the language variant in major or mild frontotemporal neurocognitive disorders is the difficulty with grammar, word-finding, or word-generation, often resulting from specific brain area damage associated with language and speech functions.
Step-by-step explanation:
Diagnostic Feature of Language Variant in Frontotemporal Neurocognitive Disorder
In the context of frontotemporal neurocognitive disorders, particularly the language variant, the diagnostic feature that stands out is the difficulty with grammar, word-finding, or word-generation. A signature characteristic of this disorder is the presence of aphasias, which refers to impairments in language and speech functions resulting from damage to important integration areas within the brain. Specifically, patients demonstrate difficulties that can lead to the inability to say certain types of words, which may be characterized by V impairment (difficulty with verbs) or N impairment (difficulty with nouns), or a V-N dissociation. In cases involving damage to certain areas of the brain, such as the insula or the middle and inferior temporal lobe, patients might experience a specific type of word usage difficulty. This presents as challenges with grammar and finding or generating the correct words during communication, which reflects the loss of certain cognitive language functions.